The Inconvenient Skeptic: The Comprehensive Guide to the Earth's Climate

by John Kehr

Eccentricity seems to be the main force for climate change over the past million years. Eccentricity has 100,000 year cycles that are part of a 400,000 year cycle. The more eccentric the Earth’s orbit, the bigger the distance from the sun the earth is between the closest and farthest distances. So a high eccentricity results in a bigger difference when the Earth is closest or farthest from the sun. If there is low eccentricity then the closest and farthest distances don't have as much difference in energy. It is all about the timing. The big factor is, how close is the Earth to the sun during the NH summer? If it is closest with high eccentricity then the NH gets lots more energy. This is what happened with the Eemian interglacial. If there is low eccentricity the Earth is less likely to get high energy. The next 100,000 years will have a lower than normal eccentricity which will prevent high insolation summers from happening. The obliquity is the tilt of the Earth. Over the course of 41,000 years the tilt of the Earth varies from about 21-25 degrees. A high tilt causes the NH to point more directly at the sun during the summer so it receives more energy during the summer. When the tilt is lower the NH less pointed at the sun and receives less. The obliquity (57) was the main factor in the early part of the current ice age when the glacial cycles matched the obliquity of the Earth. That lasted for about 1.6 million years before eccentricity became the dominant forcing fact...